Need help with transmission

You'd know it if your axles went out. My guess is an issue with the synchro assembly. Might not be engaging correctly in high range, causing it to get thrown out of engagement when you step on the go pedal.

 

Clutch slipping? Free play?

 

If you adjusted the clutch already and it is still slipping, your clutch is worn out. If so, have them replace the rear main seal regardless if it isn’t leaking when they replace the clutch. Also have them check the motor mounts since everything is out of the way. Btw, I had my transmission cooler lines replace when they did my clutch and transmission. Those cooler line get brittle in time and collapse internally.

 

Not sure what you're saying. Can you restate it?

 

I hate to mess with a seal that is not leaking. However if you are going to do that look at the engine to flywheel housing area for leakage. If your going in get it all.
Old transmission lines which have been disturbed have cost many a transmission.
Sounds like you are back to what Amodel said.

 

Low air pressure can cause slow shifting and missed engagements. Also the splitter cylinder can fill with oil causing slow shifting. It sounds like the splitter is not going into gear?? Or is it the range? Front lever or the lever on the side of the stick?